1. Field of the Invention
This invention generally relates to improvements in data storage devices for the input and output of information to a data processing system and, more particularly, to the retention of status and device identification information on a status track of each of the data storage devices and another location to provide global identification and management of interchangeable data storage devices.
2. Description of the Prior Art
The past several years have seen the growth of online workstations, the evolution of distributed processing, and the acceleration of information technology in many new application areas. The result has been an increase in the use of online data base systems and a growth in the requirement for storage capacity and increased reliability and flexibility in data storage devices.
The concepts of self-test, redundancy, cross-check verification between various sources of information and the like are well known in the art. Particularly, with the advent of complex digital computer systems used for applications such as process control or supervisory control. An example of such a system is illustrated in U.S. Pat. No. 4,032,757 to Eccles, which uses a pair of channels to continually compare the events occurring in each computer. The constant comparison allows the additional processor to quickly take over control of the process if the other processor fails. The problem with this approach is the time that the extra processor needs to begin processing after a failure. In critical processes such as in a nuclear power plant, any time lag could be unacceptable. A better approach is presented in U.S. Pat. No. 4,270,168 to Murphy et al., which uses a plurality of processors, self checks and joint answer checking to assure that each processor can assume real time utilization for another processor in the event of a failure. The increased reliability presented in these systems is a memory resident application approach that fails to handle a large data base application spanning many data storage devices.
The general configuration of a data processing system typically comprises a host processor or processors, a memory and various peripheral units. The peripheral units include terminals, printers, communications devices and data storage devices (DASD). We are concerned with the control that provides information from DASD to a data base application residing in the host processor memory. A good example of prior art approaches to this type of processing is presented in U.S. Pat. No. 3,999,163 to Levy et al., U.S. Pat. No. 4,067,059 to Derchak and U.S. Pat. No. 4,189,769 to Cook et al. These patents present various ways to enable a host to process information residing on DASD. While these patents describe production systems that readily lend themselves to data base applications, they are lacking the capability of retaining status information when a power-off occurs in an environment designed to provide high availability of DASD information.